A measuring light beam which is emitted from a line-emitting light source is produced in standard atomic absorption spectroscopy. The light source, for instance a hollow-cathode lamp, emits a line spectrum which corresponds to the resonance lines of a specific element to be determined. The measuring light beam is passed through an atomizing region in which the atoms of a sample are present in their atomic state. Such an atomizing region may, for instance, be the interior of a graphite furnace in which the sample is electrothermally atomized. In the atomizing region the measuring light beam is subjected, due to the atomic vapor, to a time-dependent specific absorption which depends on the amount of the element to be determined in the sample. The measuring light beam will then pass through a medium resolution monochromator which only allows the passage of a specific line from the line spectrum. The measuring light beam will then fall onto a single detector, normally a photomultiplier. It is only a single element which can respectively be determined in this way at one time, namely the element whose resonance lines are emitted from the light source.
Furthermore, it is known that a reference light beam is passed through the atomizing region onto a detector alternately with the measuring light beam emitted from the hollow-cathode lamp in order to compensate for the effect of background absorption. Such a reference light beam has a bandwith which is large in comparison with the line width of the hollow-cathode lamp. As a result, the reference light beam remains virtually unaffected by the specific absorption by the sample atoms.
Another way of compensating for background absorption consists of applying a strong magnetic field to the light source or the atomized sample in a periodic manner. The emitted spectral lines and the absorption lines are thereby split up due to the Zeeman effect. There is a periodic relative shift between the spectral lines absorbed by the sample atoms and the spectral lines emitted by the light source. Background absorption is normally not influenced by a magnetic field, whilst the specific atomic absorption is absent upon application of a magnetic field. The pure atomic absorption which is corrected with respect to background absorption can be determined by subtraction.
Furthermore, there are known atomic absorption spectrometers which make use of a continuous source of radiation in combination with a high-resolution spectrometer and a multitude of detector elements. In these atomic absorption spectrometers the background absorption is determined by measuring the absorption in the direct vicinity of the analysis line. The specific absorption is then determined by subtracting the background absorption determined in this way from the total absorption which was measured on the analysis wavelength. The respective spectral region in which the background is determined is selected in that the spectrum is evaluated by the person who performs the measurement.